NOTES ON TIDE-GAUGES. 8L 
- wound once a week, and the sheet changed at the same 
time, but in case a reading is required in the interval, a 
glass window is provided in the case, through which a great 
part of the cylinder F may be inspected without taking off 
the topof the case. However the whole operation of rais- 
ing the gauge, opening the case, removing the used-up 
sheet and gumming on a new one, reclosing the case and 
lowering into place, does not usually take more than 15 
minutes, and could be done in less time. 
In the machine now in use the chamber A and the tube 
D are made of vulcanite, which can be easily drilled to 
receive the fastenings for the cylinder support and the 
guide for the rod H, but the expense of making the chamber 
of this material is a serious drawback. The cost in Sydney 
was two pounds ten shillings, and the cost of a similar 
chamber in earthenware, glazed on the inside, is fifteen 
shillings. A gauge is now being made having an earthen- 
ware mercury-chamber, for the purpose of comparing the 
cost of the two materials. The float G, the rod H and the 
cylinder F are of aluminium, and the remaining fittings are 
of brass, with the exception of the steel pinion upon which 
the cylinder revolves. 
It is thought that the machine cannot be made more 
simply than the design shows, as all superfluous parts are 
omitted, with the result that the gauge cannot be put out 
of gear except by careless handling. The design of the 
pen J is such as to cause a minimum of friction on the 
cylinder Ff’, the small knob on the back being added to or 
reduced in size till the ink just flows freely from the pen. 
The copper tube is introduced to provide a connection 
between the air in the water-tight case and the outer 
atmosphere, in order that condensation may not take place 
when the case is closed on a warm day and then lowered 
into the cold water. The leaden weights are provided in 
